We review the connection between QCD and supersymmetric theories. We focus on the non-perturbative large- N (planar) correspondence between one-flavor QCD and pure supersymmetric Yang-Mills theory ([Formula: see text]). We explain how non-perturbative quantities in QCD, such as the quark condensate, can be evaluated by using the corresponding non-perturbative results in supersymmetric gauge theories. The review consists of three parts. The first part is devoted to a review of pure [Formula: see text]. In the second part we introduce "orientifold planar equivalence". The third part is devoted to the implications of planar equivalence for QCD.